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MgBrz, the experiments involving a large excess of product, ROMgBr, with the resolution of k4 and ks, the independence of the total rate behavior on initial Grignard reagent concentration at constant excess ketone concentration, and the association data. Nowhere are additional parameters, e.g., salt effects, required to fit the data to a particular mechanism. All conclusions are drawn from fundamental values, i.e., measured equilibrium constants and measured rates. It should be emphasized that all of the steps represented by eq 21-27 are important in describing the
reaction of methylmagnesium bromide with excess 2-methylbenzophenone. The same mechanistic steps hold for the reaction in excess Grignard reagent except that the steps after eq 21 become relatively unimportant. This is due to the fact that the concentrations and reactivity of ROMgCH,, G . P , and G . P 2 are relatively low compared to (CH,),Mg and CH3MgBr and, therefore, the reaction proceeds mainly by the sequence described by eq 21. When the Grignard to ketone ratio is the same or nearly the same, it is clear that the steps described by eq 22-27 once again become important.
Chemistry of Atomic Silicon. 111. Reactions of Electron Bombardment Produced Silicon Vapor with Silanes Philip S. Skell* and Peter W. Owen
Contribution f r o m the Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802. Received December 9 , 1971 Abstract: Silicon atoms were found to react with trimethylsilane, dimethylsilane, methylsilane, a n d disilane exclusively by insertion into silicon-hydrogen bonds. The resulting silenes inserted into a silicon-hydrogen bond of another substrate molecule, or polymerized to form linear and cyclic polysilanes. The electron bombardment ~~. ,silene intermediates. of solid-phase silanes at 77°K gave products derived from
T
he fact that compounds containing silicon-hydrogen bonds are notably good trapping agents for carbenes,' carbon atoms,2 and silenes3 made this class of substrates a logical choice for a study of silicon atom reactions. The cocondensation of thermally produced silicon vapor with trimethylsilane has previously been reported. Reactions of recoil silicon atoms produced by the nuclear transformation 3lP(n,~)~lSi with silane5,6 and by the transformation 30Si(r1,y)~~Siwith silane' and with silane, disilane, and trisilanes have also been reported.
Experimental Section The apparatus and procedure used was basically the same as that described for the study of carbon atom reaction^.^ Reactions were carried out by simultaneously depositing silicon vapor and a large excess of substrate on the liquid nitrogen cooled walls of an evacTorr) reaction flask. Silicon vapor was prouated (
